Release materials, such as release webs and sheets have previously been used in a wide variety of articles of manufacture typically for temporarily covering a tacky adhesive such as a pressure sensitive adhesive. Additionally, the release materials of the prior art have been used in a wide variety of manufacturing processes requiring the use of a release material to transfer an adhesive layer from one substrate to another.
However, such prior art release materials usually have a number of disadvantages. It is known to those skilled in the release material art, that release materials are provided with a coating, such as a silicone coating, to improve the release properties. However, when a release material is provided with a silicone coating and stored in roll form, a common practice, the reverse side of the release material can pick up silicone coating by offsetting. The offset silicone coating can be objectionably transferred during use of the release material. Such objectionable silicone offsetting is also known to sheet release material wherein the sheet release material, before being applied to other structures, is stacked vertically before the silicone is completely cured causing transfer or offsetting of silicone from the top surface of a lower sheet to the bottom surface of the next above sheet. The use of release coatings also requires additional process steps in order to apply the coating that adds to production costs. Furthermore, release materials of the prior art that include a release coating suffer from an increase in release force with time due to degradation of the coating integrity with use or over time.
It is also known in the prior art to decrease the release force of a release material through a reduction in contact area between the adhesive and release material. Typically, this is accomplished by creating a patterned texture on the surface of the release material that contacts the adhesive layer. The decrease in release force of these types of release materials is derived from the fact that the adhesive does not contact the entire surface area of the release material but rather only makes point or line contact with the top surface of the patterned texture. Thus, such release materials decrease release force by effectively decreasing contact area between the adhesive and the release material from area contact to point or line contact.
These types of textured release material, however, have disadvantages. The reduction of area contact to point or line contact does not provide a release material suitable for use at elevated temperatures or under compressive loads. Typically, the texture applied to the release liner is of a geometry so as to only make point contact with the adhesive. The textures are not designed to penetrate the adhesive layer as such penetration would effectively increase contact area between the adhesive and the release material beyond that of point or line contact contrary to the theory behind textured release materials. However, as compressive force is applied to textured release liners the adhesive is forced into the release liner so as to cause the adhesive to completely wet out the release liner. Thus, compressive force applied to textured release liners leads to total area contact between the release material and adhesive layer and an increase in release force.
Additionally, at elevated temperatures, adhesives can flow and migrate toward the release liner land eventually completely wetting out the release liner. The textures typically used with the release liners of the prior art are of a geometry that does not inhibit the adhesive from contacting the land of the release materials at elevated temperatures.
There are a number of processing needs requiring the use of a release material to transfer an adhesive layer from one substrate to another. New adhesives are being developed that adhere well to a wide variety of surfaces, including low energy surfaces such as for example, polypropylene and polyethylene. The aggressive adhesion of these adhesives makes them unsuitable for use with conventional release materials. Among these new adhesives are silicone adhesives for example that are not compatible with the release materials of the prior art, and are placing strong demands on release material properties. Accordingly, there exists a need in the art for improved release materials for use at elevated temperatures, under compressive loads and with modem adhesives.